Recently, along with scale expansion and growing complexity of a storage environment due to an increase of company data, thin provisioning utilizing virtual volumes (hereinafter referred to as the virtual volumes) which do not have their own storage areas has become widely used (for example, see Patent Literature 1) for the purpose of facilitation of operation management and integration of the storage environment.
With the thin provisioning, a virtual volume(s) is presented to a host system. If the host system makes write access to the virtual volume, it allocates a physical storage area for actually storing the data to the virtual volume. As a result, a volume(s) whose capacity is larger than that of the storage areas in the storage apparatus can be presented to the host system, and the storages areas in the storage apparatus can be used very efficiently.
One or more HDDs (Hard Disk Drives) constitute one RAID (Redundant Arrays of Independent Disks) group, and one or more logical volumes are defined in storage areas provided by one RAID group. Also, one or more RAID groups constitute one storage pool and each storage pool is associated with one or more virtual volumes. If write access is made from the host system to a virtual volume, a storage area in a unit(s) of a predetermined size (the storage area of this size will be hereinafter referred to as the page) is allocated from any of the logical volumes in a storage pool, which is associated with the relevant volume, to the relevant segment of the virtual volume which has been write-accessed.
In this case, by means of the conventional thin provisioning, pages may be allocated equally from a plurality of RAID groups constituting pool volumes in order of access to the virtual volume when allocating pages to the relevant segment of the virtual volume. Consequently, data is stored in a plurality of HDDs equally by allocating pages equally from the plurality of RAID groups. In this way, an attempt is made to reduce response time for write access from the host system and enhance access performance.